This invention relates to a process for a production of continuous inorganic fiber and to an apparatus therefor, and more particularly to a process for the spinning of precursory fibers of continuous inorganic fibers and to an apparatus for working the process.
Up to now, the production of continuous inorganic fibers by the steps of preparing a spinning dope composed of an organic polymer, an inorganic salt, and water, thereby obtaining precursors of fibers by dry spinning and subsequently subjecting the precursors of fibers to a heat treatment has been disclosed by GB 1470282 and GB 1360200, for example. These prior inventions have disclosed the idea of extruding the spinning dope through the spinnerets and have disclosed nothing about the shape of such spinnerets. In the ordinary dry spinning, there is generally used a spinning nozzle containing tens to hundreds of spinnerets. The spinnerets are each formed, as illustrated in cross section in FIG. 1, by boring a generally conical hole through a nozzle plate (metal plate) 1 having a thickness of 2 to 15 mm in such a manner that the hole has a diameter of 2 to 4 mm on the spinning dope inlet side 2 and a diameter of 0.1 to 0.3 mm on the spinning dope outlet side 3, respectively of the nozzle plate. An ideal dry spinning condition obtained with the spinnerets of FIG. 1 is illustrated in FIG. 2. The spinning dope 4a is extruded out of the spinneret outlet and, at the same time, stretched in the direction of the arrow by a winding machine (not shown) and dried to give rise to a fiber 5a.
The dry spinning which uses these spinnerets, however, is affected by the composition, viscosity, density, etc. of the spinning dope. It is carried out advantageously only when the spinning dope being used possesses specific properties. If the spinning dope possesses viscosity below the level of 200 poises, for example, the spinning is effected with difficulty. When the spinning dope of this viscosity is subjected to the dry spinning by the use of spinnerets of FIG. 1, the condition of spinning is as illustrated in FIG. 3. Since the spinning dope 4b assumes a semispherical shape 6 at the outlet of each of the spinnerets, the fibers 5b are formed with pronounced instability. If the spinning dope emerging from the spinnerets bulges semispherically and adheres to the nozzle plate, desired spinning can be scarcely started and the descending threads of spinning dope are liable to break before they are allowed to solidify. If any of the emerging threads of the spinning dope sustains breakage, the spinning dope freshly emerging from that particular spinneret is suffered to spread out and join the threads of spinning dope emerging from the adjacent spinnerets. Consequently, the spinning can no longer be continued. High affinity of the spinning dope for the metal of the nozzle plate and poor spinnability of the spinning dope may be possible reasons for the semispherical bulging of the spinning dope at the outlets of spinnerets illustrated in FIG. 3 and the consequent adhesion thereof to the nozzle plate.